Another possibility is a dewatering pipe. I have seen such things in the Namurian of western Co. Clare in Ireland (part of my post-grad. work on soft sediment deformation). When sands/silts express contained water, it can come out in various ways, giving rise to such features as small-scale sandstone dykes and volcanoes. What I have in mind is a pipe feeding a sand volcano. They are usually only a few cm long, partly cone-shaped, and can contain concentric layering. But, again, yours somehow does not sem quite right. Also, I don't know if they've been recorded from your locality.

I'd still lean towards root cast. Bear in mind at least some of the concentric layering could be diagenetic/concretionary, and it could be just the central (unlayered) part that represents the original root. Hence my asking if the concentric layering crosses the sedimentary layering.

It is definitely worth keeping, if only to go in the amusements box for unsuspecting visitors.

...From where you produce it and ask the visitor to ID it. If they say 'no idea', you can say 'well I can't give the game away'; if they give you a convincing ID... ...you can tell them 'well done', then go check it later